actually i believe that both issues are related: the update pack info is retrieved from the servers as you press the button, if you're having problems updating or experiencing slowness it might "freeze" waiting for the info.in this topic viewtopic.php?f=90&t=122213 you'll get the needed info to change to a faster server

Failed to fetch http://packages.linuxmint.com/dists/debian/import/i18n/Translation-en_US Unable to connect to packages.linuxmint.com:http:Failed to fetch http://packages.linuxmint.com/dists/debian/import/i18n/Translation-en Unable to connect to packages.linuxmint.com:http:Failed to fetch http://packages.linuxmint.com/dists/debian/main/i18n/Translation-en_US Unable to connect to packages.linuxmint.com:http:Failed to fetch http://packages.linuxmint.com/dists/debian/main/i18n/Translation-en Unable to connect to packages.linuxmint.com:http:Failed to fetch http://packages.linuxmint.com/dists/debian/upstream/i18n/Translation-en_US Unable to connect to packages.linuxmint.com:http:Failed to fetch http://packages.linuxmint.com/dists/debian/upstream/i18n/Translation-en Unable to connect to packages.linuxmint.com:http:Some index files failed to download. They have been ignored, or old ones used instead.

mint-choose-debian-mirrors picks the best mirror for the 3 debian repos in your sources.list, the errors you are seeing are from packages.linuxmint repo, to pick a mirror for that repo you have to follow xenopeek's topic that i linked above

[There were no mirrors in US, so I chose the one in Canada.] mintUpdate refresh was significantly faster and no 'Failed to fetch...' errors encountered and shows 'Your system is up to date'. So, I guess all is well except the 'Update Pack Info' button is still unresponsive.